Matrix-form radiation image converter

ABSTRACT

An image converter is used to make visible images produced by gamma rays or similar penetrating rays like X-rays, etc., by transforming the distribution of ray density contained in a bundle of rays carrying the image which is to be made visible, by means of a cathode and an anode spaced from the cathode. The space between the electrodes contains a gas and the electrodes are subjected to a voltage which produces electrical discharges during ray penetration at corresponding locations depending upon the rays. The cathode as well as the anode consist of a plurality of parts having large surfaces which extend at least approximately perpendicularly to the ray incoming surface of the converter, so that the electric field extends parallel to this surface. The invention is particularly characterized in that the gas is under pressure in the range of 10 at., that the applied voltage makes certain the operation in the proportional range and that parts of the anode and of the cathode are combined in rows. Rows of the cathode elements and those of the anode extend at an angle to each other, the rows being connected electrically with a device for forming an electronic intensity center which produces representable local signals for orientation of the discharge bundle striking the anode.

United States Patent 1 Reiss Dec. 30, 1975 MATRIX-FORM RADIATION IMAGECONVERTER [75] Inventor: Karl-Hans Reiss,Erlangen,

Germany [73] Assignee; Siemens Aktiengesellschaft, Munich,

Germany 22 Filed: June 5,1973

21 Appl. No.: 367,144

Primary Examiner-James W. Lawrence Assistant Examiner-Davis L. WillisAttorney, Agent, or FirmV. Alexander Sher [57] ABSTRACT An imageconverter is used to make visible images produced by gamma rays orsimilar penetrating rays like X-rays, etc., by transforming thedistribution of ray density contained in a bundle of rays carrying theimage which is to be made visible, by means of a cathode and an anodespaced from the cathode. The space between the electrodes contains a gasand the electrodes are subjected to a voltage which produces electricaldischarges during ray penetration at corresponding locations dependingupon the rays. The cathode as well as the anode consist of a pluralityof parts having large surfaces which extend at least approximatelyperpendicularly to the ray incoming surface of the converter, so thatthe electric field extends parallel to this surface. The invention isparticularly characterized in that the gas is under pressure in therange of 10 at that the applied voltage makes certain the operation inthe proportional range and that parts of the anode and of the cathodeare combined in rows. Rows of the cathode elements and those of theanode extend at an angle to each other, the rows being connectedelectrically with a device for forming an electronic intensity centerwhich produces representable local signals for orientation of thedischarge bundle striking the anode.

6 Claims, 4 Drawing Figures US. Patent Dec. 30, 1975 Sheet10f2 3,930,162

Fig.3

Fig.2

U.S. Patant Dec. 30, 1975 Sheet 2 of2 3,930,162

MATRIX-FORM RADIATION IMAGE CONVERTER This invention relates to an imageconverter for making visible images produced by gamma rays or similarpenetrating rays like X-rays etc. by transforming the distribution ofray intensity contained in the cross-section of the ray bundle carryingthe image which is to be made visible, into an image of discharge bymeans of a cathode and an anode spaced from the cathode. The spacebetween the electrodes contains a gas. The electrodes are subjected to avoltage which produces electrical discharges at locations which arestruck by the rays. The cathode as well as the anode consist of aplurality of parts the large surfaces of which extend at leastapproximately perpendicularly to the ray striking surface of theconverter, so that the electrical field extends parallel to thissurface.

Devices of this type are used in the art to change invisible imagesproduced by ionizing rays like gamma rays, X-rays etc. into a formsuitable for evaluation.

Known image converters of this type were provided as a substitute forspark image converters wherein the electrodes are plates subjected toelectrical voltage and having large surfaces extending opposite eachother. Between these plates a visible spark discharge takes placedepending upon the rays. The electrical field then extends parallel tothe rays which strike the plates perpendicularly. The efficiency issmall, however, since the path of the rays in the gas filling the spacebetween the electrodes, is small and thus their absorption is small, Aquantum change in the range of :1 is the rule. A better construction ofthis type is described in the German Pat. No. 1,764,905 which refers toelectrodes consisting of several parts the arrangement of which has theeffect of small tubes having parallel axes and located next to eachother with the counter electrode located in the center. In devices ofthis type the path of the rays can be increased when the end openings ofthe tubes are located upon a surface which receives the image producingrays. Then the electrical field extends transversely, so that ascompared to the above-mentioned spark chamber with unchangeable layerthickness concerning electrical properties (distance cathode-anode), thelayer thickness as concerns ray incidence, namely, the absorption isincreased several times depending upon the length of the tube.

A drawback of the known image converting device is that the quantumoutput is only small, particularly for the localization andrepresentation of gamma ray results, as they take place in isotopediagnosis. For these purposes other complicated devices have beenintroduced, as for example, the so-called Anger-camera. As is known, inthis camera signals are produced by several electronic multiplyingsections from scintillations produced in a luminous layer by ray actionswhich are to be made visible, the signals corresponding to theelectronic intensity point structure.

An object of the present invention is to provide a device which canserve as a gamma camera and which can produce by substantially simplermeans ray products and images which are at least comparable to those ofthe Anger-camera.

Other objects will become apparent in the course of the followingspecification.

In the accomplishment of the objectives of the present invention animage converter is used which makes visible images produced by gammarays or similar penetrating rays by transforming the distribution of rayintensity in a ray bundle carrying the image to be made visible into adischarging image by means of a cathode and a spaced anode. The spacebetween the electrodes contains a gas and the electrodes are subjectedto a voltage which produces electrical discharges during ray penetrationat the corresponding locations depending upon the rays. The cathode andthe anode consist of a plurality of parts having large surfaces whichextend at least approximately perpendicularly to the ray receivingsurface of the converter, so that the electrical field extends parallelto this surface. The present invention is particularly characterized inthat the gas is under pressure in the size of 10 at., that the appliedvoltage makes certain the operation in the proportional range and thatparts of the anode and the cathode are combined in rows, with the rowsof the cathode elements and those of the anode extending at an angle toeach other. The rows are connected electrically with a device forforming an electronic intensity center which produces image-like localsignals for orientation of the discharge bundle striking the anode.

Despite a somewhat higher expense for the operation in proportionalrange due to the height of the signal, there is the advantage that incase ofa quantum output comparable to the Anger camera and a certaindiscrimination of impulses, a more precise localization is produced. Theconstruction is much more simple. No scintillation layer is required,which usually consists of a single crystal, and it is not necessary touse many electronic multiplier stages.

Measurements which have been actually carried out have shown that, dueto the high absorption of a gas such as xenon at about 10 at., highquantum output can be expected. The upper pressure limit is basedprimarily upon the firmness of the inlet surface and lies at about 20at.. If, for example an absorption thickness of the gas layer of 10 cmis used, the following quantum efficiencies have been calculated forxenon subject to a pressure of 10 at.:

Xe keV 89% Te keV 37% I 360 keV 13% The above amounts do not considerthe release of electrons at the metal surface of the inlet window. Therean additional effect of l to 2% can take place. Iodited hydrocarbons canbe also used as similarly acting gases. Pressure must lie in theabove-mentioned range, since the number of molecules per unit volume isproportional to pressure.

According to a preferred embodiment of the present invention the casingof the converter consists of a pressure-tight container the side wallsand the bottom of which consist of steel A collimator can be placed atthe ray inlet surface which diminishes the effects of contrastdiminishing stray rays. As is known, it consists of a honeycombstructure the openings of which extend in the direction of incoming raysand which is limited by walls having a thickness of 2 to 4 mm, whichmostly consist of lead. The openings with a depth of'6O mm have adiameter of 6 mm. The inlet window for the rays, i.e., the closing ofthe openings of the collimator at their limit to the pressure tightcontainer, consists of a ray transmitting substance, such as titanium.The cover can be pulled in the form of a foil which is 1 to 2 mm thickupon the ray outlet openings of the collimaent invention provides thatthe little tubes and the inner conduits which act as electrodes shouldbe combined into n rows and n columns and guided upon 2n passages. Anadditional guide can be used for a capacitively coupled signallingplate. This arrangement provides n image prints.

Known devices, including the Anger camera, have provided differentsolutions for the discrimination and local representation of appearingimpulses. One of them is described by Kullander and assistants in thepublication Nuclear Instrum. Meth. 92 (1971 no. 1, page 141. When thisdevice is used within the framework of the present invention the rowsand sections of the tube arrangement are guided upon transit chains.When an impulse arrives it produces initially a starting signal upon asignalling plate. With this starting signal two clocks are started whichdetermine the running time of a chain for the x direction and the ydirection. These running times are used as a measure for the coordinatesand can be used for representation upon an oscillograph. The impulseheight ofeach impulse is independently examined by a discriminator. Thusonly those impulses are counted to which the discriminator was set,namely those the height of which corresponds to the required gammaenergy. The representation can take place in a known manner upon adisplay device or in a magnetic core matrix.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawingsshowing by way of example only, preferred embodiments of the inventiveidea.

In the drawings:

FIG. 1 is a diagrammatic view showing a spark chamber of the presentinvention provided with honeycombed cathodes.

FIG. 2 shows in perspective a part of the device of FIG. 1 andillustrates specifically the hexagonal crosssection of the tubes in thelongitudinal axes of which the anodes in the shape of round pins arelocated.

FIG. 3 shows in perspective a constructively simple device of thepresent invention wherein the cathodes are plateshaped and the anodesare introduced as rods in the spaces between these plates.

FIG. 4 is a circuit diagram of an electronic switch arrangement fordetermining gravity points of spots which are struck by rays accordingto the device of the present invention.

FIG. 1 shows a pressure-tight chamber 1 provided with faucets la and 1band containing anodes 2 lying at the positive pole of the source 3 ofdirect voltage. The negative pole of the source 3 is connected with thecathode 4 consisting of a plurality of little tubes combined in rowswhich are electrically insulated from each other transversely to therows by intermediate layers 5 of mica which are 0.2 mm thick. The littlecathode tubes are produced from adjacently located strips 7 which are100 mm wide and consist of brass or heavy metal sheets 0.30 mm thick(FIG. 2), which have a profile of alternately raised and pressed downportions each in the shape of one half hexagon. When the sheets areplaced together hexagonal tubes of honeycomb structure are produced witha diameter of 6 mm. The anode is placed in the shape of rods 8 in thelongitudinal axis of the hexagonal tubes and is held at the beginningand end of the tubes by insulating pieces 9 and 10 of acrylic glass. Inthe tubes of the cathode 4 there is a gaseous atmosphere consisting ofxenon for the introduction, refilling or exchange of which in the spaceof the casing 1 there are provided openings 9a and 10a in the holdingpieces 9 and 10 at the beginning and end of the cathode tubes.

When voltage is applied for operation in the proportional range, in thepresent case about 8 kV, and when ionized rays strike in the directionof arrows 6, at those locations wherein rays drop into the tubes thereis a discharge depending upon the number of absorbed quantum. Thesedischarges produce signals which are tranformed into a visible picturein the analyzing device 10' the details of which are shown in FIG. 4.

FIG. 3 shows an embodiment of the present invention which isparticularly advantageous due to its simple construction wherein thecathode consists of plates 11 placed next to each other. The plates havea width of mm, a thickness of 0.3 mm and consist of a metal middleordinal number, in this case nickel. The plates 11 have a spacing of 3mm which is maintained at upper and lower edges of the plates by spaceholders 12, 13 of insulated plastic, namely, acrylic glass. The plasticholds metal rods 14 which are the anodes, with their longitudinal axesparallel to the plates 11 and to each other. The rods at their lowerends extend through the holders 13 and at their upper side are connectedto the insulating holder 12. The rods 14 consist of rust free steel,have a circular cross-section with a diameter of 1 mm and a length whichcorresponds to the plate width up to about 0.5 mm. The applied voltageamounts to about 6 kV.

The operation of the embodiment of the present invention shown in FIG. 3is substantially the same as that of the construction of FIGS. 1 and 2.The sole difference is that in the construction of FIG. 3 no separatetubes are formed. In this construction also the rays penetrate throughthe cathode plates 11 and the anode rods 14 into the intermediate spacewhich is the gas chamber filled in this construction with xenon andsubjected to a pressure of 8 at..

The strips 7 of FIGS. 1 and 2 or the plates 11 of FIG. 3 form alongitudinally extending cathode constituting a row over which the imagearea runs. Transversely thereto extend the electrical connecting lines15 to 20 of the rods 8 and the connecting lines 21 to 29 of the rods 14(FIG. 3). The connections of the cathodes are indicated by numerals 30to 33 in FIG. 2 and by numerals 34 to 36 in FIG. 3. It is apparent thatwhen the lines 15 to 20 are connected with lines 30 to'33 and the lines21 to 29 are connected with lines 34 to 36 the derived values canproduce significant x-y signals indicating the section of the rows bycorresponding arrangement of specific strips 7 or plates 11 and aspecific row of pins 8 or 14. Since these signals follow one after theother it I is also possible to produce a discrimination of the height ofindividual signals in a known manner.

The determination of the striking location of the ray spot or its centertakes place according to FIG. 4 in gamma cameras in a manner known perse by analogous gravity point formation. For better clarity ofillustration FIG. 4 shows only a few of the electrode rows present inthe described example and corresponding to lines to and 30 to 33, aswell as lines 21 to 29 and 34 to 36; the rows are indicated in FIG. 4 as37 to 41 and 42 to 46. They are connected by high ohmic resistances 47and 48 with corresponding source 49 of direct voltages. As shown in FIG.4, the discharges produced by the ray bundle penetrating into the spot50 are collected in the rows 37 to 41 and in rows 42 to 46 extendingtransversely thereto. These discharges are strengthened in chargereceiving amplifiers 51 to 55 and 56 to 60 to form signals capable offurther treatment. The signals X, which pertain to i rows 42 to 46, theamount of which corresponds to part of the charge carriers from the spot50 collected on one side, are considered in a coordinate network 61corresponding to the location of the pertaining electrode strip, i beingthe number of continuously counted rows while x is the x-coordinate.During the examination a factor a, is impressed upon the signal X,- fromthe resistances 62 to 71 with the use ofa voltage divider. By a suitableselection of resistances 62 to 71 the factors a,- form discretecoordinate values of corresponding rows 1' in the x direction. Assuitable selection resistances are here used produced by voltagedividers the ratio of which corresponds to a,- and results in i/i Here iis the running number of strips and i is the greatest available numberof strips. Furthermore the sums of both resistances of each voltagedivider are equal.

The examined signals a x are summed up in a sum amplifier 72. A signal 2a x is produced; then after division in the quotient former 73 by thesum signal of all untreated signals x,- produced in the sum amplifier 74the following normed local signal results:

2 n x, E x,-

In the presented example the X-signal and the Y-signal formed incorresponding manner by the use of anode rows 37 to 41 in coordinatenetwork 75 (identical to 61) are supplied to the imaging element 76 ofan X-Y oscilloscope and are brightly felt by a Z signal which isproduced by impulse high discrimination of untreated sum signal 2 x; inone channel discriminator 77. Then the gravity point of the spot 50 ofaray bundle striking the devices of FIGS. 1, 2 or 3 is produced in the XYdiagram of the element 76. This corresponds to the 6 location in thedevice of the original absorption location of a gamma quanta of theenergy determined by the discriminator 77, so that the desired visiblerepresentation is produced.

I claim:

1. A proportional radiation image converter for making visible imagesproduced by gamma rays, comprising a container having a ray inletsurface and, inside the container, in combination, a matrix of detectorcells, said matrix comprising two groups of conductors, the conductorsof one group being anode members and spaced from the conductors of theother group which are cathode members, the space between the groupsbeing filled with gas having substantially a pressure of 10 at., theconductors in the groups forming rows with rows of the one groupextending at an angle to the rows of the other group, the conductivemember of the group belonging to cathode members substantiallyencircling one of the conductors of the other of said groups, and thusforming one of said cells extending substantially perpendicularly to theray inlet surface, and means for separately detecting an electricalsignal from each of said conductors and for indicating the cell addressof a gas-ionizing incident in the detector; said cathode memberscomprising electrically conductive strips which are insulated from oneanother; said anode members comprising electrically conductive rodsdisposed between and insulated from said cathode members.

2. An image converter according to claim 1, wherein the rows of cathodemembers and the rows of anode members extend at right angles to eachother.

3. An image converter according to claim 1, wherein said means comprisean impulse high disciminator.

4. The device of claim 1, wherein said cathode strips are in the form offlat plates.

5. The device of claim 1, wherein said cathode strips each have thecross-section of a half of a hexagon with said strips confronting oneanother so that said half hexagonal configurations confront one anotherto define a full hexagonal shape; said anode rods being disposed at thecenter of each of said hexagonal tubes defined by said half hexagonalcross-sectional shapes of said cathode strips.

6. The device of claim 1, wherein each of said cathode strips has awidth of from to millimeters and wherein said strips are separated fromone another by a distance of from 3 to 6 millimeters.

1. A proportional radiation image converter for making visible imagesproduced by gamma rays, comprising a container having a ray inletsurface and, inside the container, in combination, a matrix of detectorcells, said matrix comprising two groups of conductors, the conductorsof one group being anode members and spaced from the conductors of theother group which are cathode members, the space between the groupsbeing filled with gas having substantially a pressure of 10 at., theconductors in the groups forming rows with rows of the one groupextending at an angle to the rows of the other group, the conductivemember of the group belonging to cathode members substantiallyencircling one of the conductors of the other of said groups, and thusforming one of said cells extending substantially perpendicularly to theray inlet surface, and means for separately detecting an electricalsignal from each of said conductors and for indicating the cell addressof a gas-ionizing incident in the detector; said cathode memberscomprising electrically conductive strips which are insulated from oneanother; said anode members comprisIng electrically conductive rodsdisposed between and insulated from said cathode members.
 2. An imageconverter according to claim 1, wherein the rows of cathode members andthe rows of anode members extend at right angles to each other.
 3. Animage converter according to claim 1, wherein said means comprise animpulse high disciminator.
 4. The device of claim 1, wherein saidcathode strips are in the form of flat plates.
 5. The device of claim 1,wherein said cathode strips each have the cross-section of a half of ahexagon with said strips confronting one another so that said halfhexagonal configurations confront one another to define a full hexagonalshape; said anode rods being disposed at the center of each of saidhexagonal tubes defined by said half hexagonal cross-sectional shapes ofsaid cathode strips.
 6. The device of claim 1, wherein each of saidcathode strips has a width of from 90 to 100 millimeters and whereinsaid strips are separated from one another by a distance of from 3 to 6millimeters.